Light emitting device and light emitting device package

ABSTRACT

A light emitting device, a method of manufacturing the same, a light emitting device package, and a lighting system are disclosed. The light emitting device may include a first conductive semiconductor layer, a second conductive semiconductor layer, and an active layer interposed between the first and second conductive semiconductor layers. The first conductive semiconductor layer, the active layer, and the second conductive semiconductor layer may include Al. The second conductive semiconductor layer may have Al content higher than Al content of the first conductive semiconductor layer. The first conductive semiconductor layer may have Al content higher than Al content of the active layer.

This application is a continuation application of U.S. Pat. No.8,314,414, issue date Nov. 20, 2012, which claims priority under 35U.S.C. §119(a) of Korean Patent Application No. 10-2009-0101959 filed onOct. 26, 2009, which are hereby incorporated by reference in theirentirety as if fully set forth herein.

BACKGROUND

The embodiment relates to a light emitting device, a method ofmanufacturing the same, a light emitting device package, and a lightingsystem.

A light emitting diode (LED) is a semiconductor light emitting devicethat converts current into light. Recently, the brightness of the LEDhas increased, so that the LED has been employed as a light source fordisplay devices, vehicles, or lighting devices. In addition, the LED canrepresent a white color having superior light efficiency by employingphosphors or combining LEDs having various colors.

The brightness of the LED is dependant on various conditions such as thestructure of an active layer, a light extraction structure sufficient toeffectively extract light to the outside, a semiconductor material usedin the LED, a chip size, and the type of molding member surrounding theLED.

SUMMARY

An exemplary embodiment provides a light emitting device capable ofreducing leakage current, a method of manufacturing the same, a lightemitting device package, and a lighting system,

An exemplary embodiment provides a light emitting device having asuperior current spreading effect, a method of manufacturing the same, alight emitting device package, and a lighting system.

An exemplary embodiment provides a light emitting device having superiorcrystalline, a method of manufacturing the same, a light emitting devicepackage, and a lighting system.

An exemplary embodiment provides a light emitting device having improvedinternal quantum efficiency, a method of manufacturing the same, a lightemitting device package, and a lighting system.

An exemplary embodiment provides a light emitting device having areduced piezoelectric effect, a method of manufacturing the same, alight emitting device package, and a lighting system.

According to an exemplary embodiment, a light emitting device mayinclude a first conductive semiconductor layer, a second conductivesemiconductor layer, and an active layer interposed between the firstand second conductive semiconductor layers. The first conductivesemiconductor layer, the active layer, and the second conductivesemiconductor layer may include Al. The second conductive semiconductorlayer may have Al content higher than Al content of the first conductivesemiconductor layer. The first conductive semiconductor layer may haveAl content higher than Al content of the active layer.

According to an exemplary embodiment, a light emitting device packagemay include a package body, first and second electrode layers mounted onthe package body, a light emitting device provided on the package bodyand electrically connected to the first and second electrode layers. Thelight emitting device may include a first conductive semiconductorlayer, a second conductive semiconductor layer and an active layerinterposed between the first and second conductive semiconductor layers.The first conductive semiconductor layer, the active layer, and thesecond conductive semiconductor layer may include Al, the secondconductive semiconductor layer may have Al content higher than Alcontent of the first conductive semiconductor layer, and the firstconductive semiconductor layer may have Al content higher than Alcontent of the active layer.

According to an exemplary embodiment, a lighting system may include asubstrate, and a light emitting module including a light emitting deviceprovided on the substrate. The light emitting device may include a firstconductive semiconductor layer, a second conductive semiconductor layer,and an active layer interposed between the first and second conductivesemiconductor layers. The first conductive semiconductor layer, theactive layer, and the second conductive semiconductor layer may includeAl, the second conductive semiconductor layer may have Al content higherthan Al content of the first conductive semiconductor layer, and thefirst conductive semiconductor layer may have Al content higher than Alcontent of the active layer.

According to an exemplary embodiment, a method of manufacturing a lightemitting device may include forming a first conductive semiconductorlayer including Al, forming an active layer including Al on the firstconductive semiconductor layer, and forming a second conductivesemiconductor layer which may include Al on the active layer. The secondconductive semiconductor layer may have Al content higher than Alcontent of the first conductive semiconductor layer, and the firstconductive semiconductor layer may have Al content higher than Alcontent of the active layer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view showing a light emitting device according to anexemplary embodiment;

FIG. 2 is a sectional view showing a lateral type light emitting devicemanufactured based on the light emitting device 100 of FIG. 1;

FIG. 3 is a sectional view showing a vertical type light emitting devicemanufactured based on the light emitting device of FIG. 1;

FIG. 4 is a sectional view showing a light emitting device packageincluding a light emitting device according to an exemplary embodiment;

FIG. 5 is a view showing a backlight unit including a light emittingdevice or a light emitting device package according to an exemplaryembodiment; and

FIG. 6 is a perspective view showing a lighting system including a lightemitting device or a light emitting device package according to anexemplary embodiment.

DETAILED DESCRIPTION OF THE EMBODIMENTS

In the description of the embodiments, it will be understood that, whena layer (or film), a region, a pattern, or a structure is referred to asbeing “on” or “under” another substrate, another layer (or film),another region, another pad, or another pattern, it can be “directly” or“indirectly” on the other substrate, layer (or film), region, pad, orpattern, or one or more intervening layers may also be present. Such aposition of the layer has been described with reference to the drawings.

The thickness and size of each layer shown in the drawings may beexaggerated, omitted or schematically drawn for the purpose ofconvenience or clarity. In addition, the size of elements does notutterly reflect an actual size.

Hereinafter, a light emitting device according to an embodiment and amethod of manufacturing the same will be described with reference toaccompanying drawings.

FIG. 1 is a view showing a light emitting device 100 according to anexemplary embodiment.

Referring to FIG. 1, the light emitting device 100 may include asubstrate 110, a buffer layer 115, an undoped semiconductor layer 120, afirst conductive semiconductor layer 130, an active layer 140, and asecond conductive semiconductor layer 150.

The buffer layer 115, the undoped semiconductor layer 120, the firstconductive semiconductor layer 130, the active layer 140, and the secondconductive semiconductor layer 150 may be formed on the substrate 110through a chemical vapor deposition (CVD) scheme, a molecular beamepitaxy scheme (MBE), a sputtering scheme, or a hybrid vapor phaseepitaxy (HVPE) scheme, but the embodiment is not limited thereto.

The substrate 110 may include at least one of sapphire (Al₂O₃), SiC, Si,GaAs, GaN, ZnO, Si, GaP, InP, or Ge.

The buffer layer 115 may be formed on the substrate 110. The bufferlayer 115 may be formed to reduce a lattice constant difference betweenthe substrate 110 and the first conductive semiconductor layer 130.

The buffer layer 115 may include aluminum (Al). For example, the bufferlayer 115 may have a composition formula of Al_(x)Ga_(1-x)N (0.5≦x≦1),in which the x is in the range of about 0.5 to 1, and, preferably, hasabout 0.8. The buffer layer 115 includes Al having a composition ratiogreater than or equal to that of Ga. However, the buffer layer 115 mayhave various materials.

The buffer layer 115 has a growth temperature in the range of about1000° C. to about 1200° C. Preferably, the buffer layer 115 may have agrowth temperature of about 1100° C. The growth temperature is higherthan that of a buffer layer including GaN without Al.

Since Al has a composition ratio higher than that of Ga in the bufferlayer 115, and the buffer layer 115 has a high growth temperature in therange of about 1000° C. to about 1200° C., the buffer layer 115 may begrown with superior crystalline. Accordingly, the lattice constantdifference between the buffer layer 115 and the substrate 110 can beeffectively reduced, and defects or dislocation of the buffer layer 115can be reduced.

For example, the buffer layer 115 may have a dislocation density in therange of about 10⁸ lots/cm² to 3×10⁸ lots/cm². Different from aconventional buffer layer having a dislocation density of about 7×10⁹lots/cm², the buffer layer 115 has a lower dislocation density.

The undoped buffer layer 120 may be formed on the buffer layer 115. Theundoped semiconductor layer 120 is not doped with N-type or P-typedopants, so that the undoped semiconductor layer 120 may have electricalconductivity significantly lower than that of the first and secondconductive semiconductor layers 130 and 150. For example, the undopedsemiconductor layer may include a layer having a composition formula ofAl_(x)Ga_(1-x)N (0<x≦0.05), in which the x is in the range of about 0 to0.05, and, preferably, may be about 0.03. However, the embodiment is notlimited thereto, and the undoped semiconductor layer 120 may not includeAl.

The undoped semiconductor layer 120 has a growth temperature in therange of about 1050° C. to about 1150° C. Preferably, the undopedsemiconductor layer 120 may have a growth temperature of about 1080° C.

The undoped semiconductor layer 120 may have a first thickness to havesufficient crystalline so that the first and second conductivesemiconductor layers 130 and 150 and the active layer 140 can be grownwithout defects and dislocation.

The undoped semiconductor layer 120 includes Al, and is formed on thebuffer layer 115 having superior crystalline. Accordingly, the firstthickness of the undoped semiconductor layer 120 may be in the range ofabout 0.5 μm to 1 μm as compared with the undoped semiconductor layer120 formed on a conventional buffer layer and having a thickness ofabout 2 μm.

Since the undoped semiconductor layer 120 has the first thickness, themanufacturing cost of the light emitting device 100 can be reduced, andthe thickness of the light emitting device 100 can be reduced.

Meanwhile, at least one of the buffer layer 115 or the undopedsemiconductor layer 120 may be formed, or none of the buffer layer 115and the undoped semiconductor layer 120 may be formed.

A light emitting structure is formed on the undoped semiconductor layer120, and may include the first conductive semiconductor layer 130, theactive layer 140, and the second conductive semiconductor layer 150. Thelight emitting structure may include Al. The second conductivesemiconductor layer 150 may have an Al content higher than that of thefirst conductive semiconductor layer 130, and the first conductivesemiconductor layer 130 may have an Al content higher than that of theactive layer 140. Hereinafter, the light emitting structure will bedescribed in detail.

The first conductive semiconductor layer 130 may be formed on theundoped semiconductor layer 120. For example, the first conductivesemiconductor layer 130 may include an N-type semiconductor layer, andinclude a material having a composition formula of Al_(x)Ga_(1-x)N(0.02≦x≦0.08). In addition, the first conductive semiconductor layer 130may be doped with N-type dopants such as Si, Ge, and Sn. The x may havea value in the range of about 0.02 to about 0.08, and, preferably, mayhave a value of about 0.05. The first conductive semiconductor layer 130may have various materials.

The growth temperature of the first conductive semiconductor layer 130may be in the range of about 1000° C. to about 1200° C., and,preferably, may be about 1100° C.

Since the first conductive semiconductor layer 130 may include Al, thefirst conductive semiconductor layer 130 may have a higher band gap andhigher electron mobility as compared with those of a GaN layer withoutAl.

Accordingly, charges can be effectively spread throughout the wholeregion of the first conductive semiconductor layer 130, so that superiorcurrent spreading can be represented. Accordingly, the light emissionefficiency of the light emitting device 100 can be improved.

In addition, since the first conductive semiconductor layer 130 may havea high band gap, the leakage current of the light emitting device 100can be reduced.

The active layer 140 may be formed on the first conductive semiconductorlayer 130. Electrons (or holes) injected through the first conductivesemiconductor layer 130 may be recombined with holes (or electrons)injected through the second conductive semiconductor layer 150 at theactive layer 140, so that the active layer 140 may emit the light basedon the band gap difference of the energy band according to materials ofthe active layer 140.

The active layer 140 may have a single quantum well structure or amulti-quantum well structure. Although the embodiment is described inthat the active layer 140 has a multi-quantum well structure, theembodiment is not limited thereto.

The active layer 140 may include a plurality of barrier layers 140 a,140 c, and 140 e, and a plurality of quantum well layers 140 b and 140 dinterposed between adjacent well layers among the well layers 140 a, 140c, and 140 e. The active layer 140 may have various stack structures.

The quantum well layers 140 b and 140 d may have a composition formulaof Al_(x)In_(y)Ga_(1-x-y)N (0≦x≦0.005, 0.1≦y≦0.3). The growthtemperature of the quantum well layers 140 b and 140 d may be in therange of about 680° C. to about 750° C., and, preferably, may be about720° C. In the composition formula, the x is in the range of about 0 toabout 0.005, and, preferably, may be about 0.001. In addition, the y isin the range of about 0.1 to about 0.3, and, preferably, may be about0.2.

A composition ratio of Al and indium (In) in the quantum well layers 140b and 140 d is adjusted, so that the conglomeration degree of In can beadjusted. In other words, In may be conglomerated by a predeterminedamount to contribute to light emission. Accordingly, the compositionratio of Al and In may be adjusted in the quantum well layers 140 b and140 d, so that the conglomeration degree of In can be adjusted.Accordingly, an amount of In actually contributing to light emission maybe increased, so that the internal quantum efficiency of the lightemitting device 100 can be improved.

Each quantum well layer 140 b or 140 d may have a stack structure ofmultiple layers. For example, each quantum well layer 140 b or 140 d mayinclude a first layer 140 ba or 140 da which may include Al and a secondlayer 140 bb or 140 db without Al on the first layer 140 ba or 140 da.

In other words, the first layers 140 ba and 140 da may include AlInGaN,and the second layers 140 bb and 140 db may include InGaN layers. Inthis case, the first layers 140 ba and 140 da have a thickness of about5 Å, and the second layers 140 bb and 140 db may have a thickness ofabout 15 Å, but the embodiment is not limited thereto.

The barrier layers 140 a, 140 c, and 140 e may have a compositionformula of Al_(x)Ga_(1-x)N (0.01≦x≦0.03). The growth temperature of thebarrier layers 140 a, 140 c, and 140 e is in the range of about 820° C.to about 880° C., and, preferably, may be 850° C. In the compositionformula, the x is in the range of 0.01 to 0.03, and, preferably, may be0.02.

The composition ratio of Al in the barrier layers 140 a, 140 c, and 140e is adjusted to change a band gap, so that the operating voltage can beadjusted. In addition, the low current characteristic of the lightemitting device 100 can be improved, so that leakage current can bereduced.

In addition, since the stack structure of the plural quantum well layers140 b and 140 d and the plurality of barrier layers 140 a, 140 c, and140 e may include Al, so that light loss caused by a piezoelectriceffect can be reduced.

Meanwhile, a clad layer may be formed on and/or under the active layer140.

The second conductive semiconductor layer 150 may be formed on theactive layer 140. The second conductive semiconductor layer 150 mayinclude a P-type semiconductor, and may include a material having acomposition formula of Al_(x)Ga_(1-x)N (0.1≦x≦0.3). In addition, thesecond conductive semiconductor layer 150 is doped with P-type dopantssuch as Mg and Ba. In the composition formula, the x has a value in therange of about 0.1 to about 0.3, and, preferably, may have a value ofabout 0.2. However, the second conductive semiconductor layer 150 mayhave various materials.

The growth temperature of the second conductive semiconductor layer 150may be in the range of about 900° C. to 1050° C., and, preferably, maybe about 960° C.

Since the second conductive semiconductor layer 150 may include Al, thesecond conductive semiconductor layer 150 may have superior crystalline.

Meanwhile, the second conductive semiconductor layer 150 may have astack structure of multiple layers. For example, the second conductivesemiconductor layer 150 may include a first layer 150 a without Al onthe active layer 140, a second layer 150 b placed on the first layer 150a and including Al, and a third layer 150 c without Al placed on thesecond layer 150 b.

The second layer 150 b may include an AlGaN layer, and the first andthird layers 150 a and 150 c may include a GaN layer. In this case, thesecond layer 150 b may have a thickness in the range of about 800 Å toabout 1200 Å, and, preferably, may have a thickness of about 1000 Å. Thefirst and third layers 150 a and 150 c may have a thickness in the rangeof about 200 Å to about 300 Å, and, preferably, may have a thickness ofabout 250 Å.

As described above, if the second conductive semiconductor layer 150includes a plurality of layers, since an AlGaN layer may have superiorcrystalline, even a GaN layer formed on the AlGaN layer may havesuperior crystalline. Accordingly, when comparing with a secondconductive semiconductor layer including only a GaN layer, the secondconductive semiconductor layer 150 may have superior crystalline.

In addition, since the second conductive semiconductor layer 150 mayhave superior crystalline, doping can be easily performed with respectto the second conductive semiconductor layer 150.

In contrast, the first conductive semiconductor layer 130 may be dopedwith P-type dopants, and the second conductive semiconductor layer 150may be doped with N-type dopants. In addition, a third conductivesemiconductor layer (not shown) doped with N-type dopants or P-typedopants may be additionally formed on the second conductivesemiconductor layer 150. Accordingly, the light emitting structure mayhave at lest one of N-P, P-N, N-P-N, and P-N-P junction structures, butthe embodiment is not limited thereto.

FIG. 2 is a sectional view showing a lateral type light emitting device100A manufactured based on the light emitting device 100 of FIG. 1.

Referring to FIGS. 1 and 2, the lateral type light emitting device 100Amay be formed by performing Mesa etching with respect to the lightemitting device 100 of FIG. 1 to expose a portion of the firstconductive semiconductor layer 130. Thereafter, a first electrode 180may be formed on the first conductive semiconductor layer 130.

A transparent electrode layer 160 may be formed on the second conductivesemiconductor layer 150. The transparent electrode layer 160 includes atleast one of ITO, IZO(In—ZnO), GZO(Ga—ZnO), AZO(Al—ZnO), AGZO(Al—GaZnO), IGZO(In—Ga ZnO), IrO_(x), RuO_(x), RuO_(x)/ITO, Ni/IrO_(x)/Au, orNi/IrO_(x)/Au/ITO, but the embodiment is not limited thereto. Thetransparent electrode 160 allows the second conductive semiconductorlayer 150 to make ohmic contact with the second electrode 170.

A reflective electrode layer may be formed instead of the transparentelectrode 160, and the reflective electrode may include at least one ofAg having high reflectance, alloy of Ag, Al, or alloy of Al.

A second electrode 170 may be formed on the transparent electrode layer160 to supply power to the lateral type light emitting device 100Atogether with the first electrode 180.

FIG. 3 is a sectional view showing an exemplary vertical type lightemitting device 100B manufactured based on the light emitting device100.

Referring to FIGS. 1 and 3, the vertical type light emitting device 100Bmay be formed by forming a reflective layer 260 and a conductive supportmember 270 under the second conductive semiconductor layer 150 of thelight emitting device 100 of FIG. 1, and removing the substrate 110.

The reflective layer 260 may be formed under the second conductivesemiconductor layer 150.

The reflective layer 260 may include at least one of Ag, alloy of Ag,Al, alloy of Al, Pt, or alloy of Pt.

The conductive support member 270 may be formed on the reflective layer260 to supply power to the vertical type light emitting device 100B.

The conductive support member 270 may include at least one of Ti, Cr,Ni, Al, Pt, Au, W, Cu, Mo, or a semiconductor substrate implanted withimpurities.

Meanwhile, an adhesion layer (not shown) may be additionally formedbetween the conductive support member 270 and the reflective layer 160to improve interfacial adhesive strength between the two layers. Inaddition, an ohmic layer (not shown) may be additionally formed betweenthe second conductive semiconductor layer 150 and the reflective layer260 to allow the second conductive semiconductor layer 150 to make ohmiccontact with the reflective layer 260.

The substrate 110 may be removed through a laser lift off (LLO) processor an etching process, but the embodiment is not limited thereto.

After the substrate 110 has been removed, portions of the buffer layer115, the undoped semiconductor layer 120, and the first conductivesemiconductor layer 130 may be removed through an etching process suchas Inductively Coupled Plasma/Reactive Ion Etching (ICP/RIE) process,but the embodiment is not limited thereto.

After the substrate 110 has been removed, a first electrode 280 may beformed on one of the first conductive semiconductor layer 130, thebuffer layer 115, and the undoped semiconductor layer 120 that areexposed. According to an exemplary embodiment, after both of the bufferlayer 115 and the undoped semiconductor layer 120 have been removed, afirst electrode layer may be formed on the first conductivesemiconductor layer 130. The first electrode 280 supplies power to thevertical type light emitting device 100B together with the conductivesupport member 270.

An exemplary embodiment can provide a light emitting device capable ofreducing leakage current.

An exemplary embodiment can provide a light emitting device having asuperior current spreading effect.

An exemplary embodiment can provide a light emitting device havingsuperior crystalline.

An exemplary embodiment can provide a light emitting device havingimproved internal quantum efficiency.

An exemplary embodiment can provide a light emitting device having areduced a piezoelectric effect.

FIG. 4 is a sectional view showing a light emitting device packageincluding the light emitting device according to an exemplaryembodiment.

Referring to FIG. 4, the light emitting device package according to theexemplary embodiment includes a body 10, first and second electrodelayers 31 and 32 formed on the body 10, the light emitting device 100Bprovided on the body 10 and electrically connected to the first andsecond electrode layers 31 and 32 and a molding member 40 that surroundsthe light emitting device 100B.

The body 10 may be a conductive substrate including silicon, syntheticresin, or metallic material, and may have a cavity with an inclinedlateral surface.

The first and second electrode layers 31 and 32 may be electricallyisolated from each other to supply power to the light emitting device100B. In addition, the first and second electrode layers 31 and 32 mayreflect the light emitted from the light emitting device 100B to improvethe light efficiency and dissipate heat generated from the lightemitting device 100B to the outside.

The light emitting device 100B can be installed on the body 10 or thefirst or second electrode layer 31 or 32.

The light emitting device 100B may be electrically connected to thefirst and second electrode layers 31 and 32 through one of a wirescheme, a flip-chip scheme, or a die bonding scheme. According to anexemplary embodiment, in the light emitting device 100B, the firstelectrode 280 may electrically connected to the first electrode layer 31through a wire, and directly make contact with the second electrodelayer 32 to be connected to the second electrode 32, but the embodimentis not limited thereto.

The molding member 40 may surround the light emitting device 100B toprotect the light emitting device 100B. In addition, the molding member40 may include phosphors to change the wavelength of the light emittedfrom the light emitting device 100B.

A plurality of light emitting device packages according to an exemplaryembodiment are arrayed on a substrate, and a light guide plate, a prismsheet, a diffusion sheet, and a fluorescence sheet, which form anoptical member, may be provided on the path of light emitted from thelight emitting device package. The light emitting device package, thesubstrate, and the optical member may constitute a backlight unit or alighting system. For example, the lighting system may include thebacklight unit, the lighting system, an indicator, a lamp, and a streetlight.

FIG. 5 is a view showing a backlight unit 1100 including a lightemitting device or a light emitting device package according to anexemplary embodiment. The backlight unit 1100 of FIG. 5 is one exampleof the lighting system, but the embodiment is not limited thereto.

Referring to FIG. 5, the backlight unit 1100 may include a bottom cover1140, a light guide member 1120 installed in the bottom cover 1140, anda light emitting module 1110 installed at one side or on the bottomsurface of the light guide member 1120. In addition, a reflective sheet1130 is disposed under the light guide member 1120.

The bottom cover 1140 may have a box shape having a top surface beingopen to receive the light guide member 1120, the light emitting module1110 and the reflective sheet 1130 therein. In addition, the bottomcover 1140 may include metallic material or resin material, but theembodiment is not limited thereto.

The light emitting module 1110 may include a substrate 700 and aplurality of light emitting device packages 600 installed on thesubstrate 700. The light emitting device packages 600 may provide thelight to the light guide member 1120. According to an exemplaryembodiment, although the light emitting module 1110 may include thelight emitting device packages 600 provided the substrate 700, a lightemitting device according to the embodiment may be directly installed inthe light emitting module 1110.

As shown in FIG. 5, the light emitting module 1110 may be installed onat least one inner side of the bottom cover 1140 to provide the light toat least one side of the light guide member 1120.

In addition, the light emitting module 1110 can be provided under thebottom cover 1140 to provide the light toward the bottom surface of thelight guide member 1120. Such an arrangement can be variously changedaccording to the design of the backlight unit 1100 and the embodiment isnot limited thereto.

The light guide member 1120 may be installed in the bottom cover 1140.The light guide member 1120 may convert the light emitted from the lightemitting module 1110 into the surface light to guide the surface lighttoward a display panel (not shown).

The light guide member 1120 may include a light guide plate. Forinstance, the light guide plate can be manufactured by using acryl-basedresin, such as polymethyl methacrylate (PMMA), polyethyleneterephthalate (PET), polycarbonate (PC), COC or polyethylene naphthalate(PEN) resin.

An optical sheet 1150 may be provided over the light guide member 1120.

The optical sheet 1150 may include at least one of a diffusion sheet, alight collection sheet, a brightness enhancement sheet, or a fluorescentsheet. For instance, the optical sheet 1150 may have a stack structureof the diffusion sheet, the light collection sheet, the brightnessenhancement sheet, and the fluorescent sheet. In this case, thediffusion sheet may uniformly diffuse the light emitted from the lightemitting module 1110 such that the diffused light can be collected on adisplay panel (not shown) by the light collection sheet. The lightoutput from the light collection sheet may be randomly polarized and thebrightness enhancement sheet may increase the degree of polarization ofthe light output from the light collection sheet. The light collectionsheet may include a horizontal and/or vertical prism sheet. In addition,the brightness enhancement sheet may include a dual brightnessenhancement film and the fluorescent sheet may include a transmissiveplate or a transmissive film including phosphors.

The reflective sheet 1130 can be disposed under the light guide member1120. The reflective sheet 1130 may reflect the light, which is emittedthrough the bottom surface of the light guide member 1120, toward thelight exit surface of the light guide member 1120.

The reflective sheet 1130 may include resin material having highreflectivity, such as PET, PC, or PVC resin, but the embodiment is notlimited thereto.

FIG. 6 is a perspective view showing a lighting system 1200 including alight emitting device or a light emitting device package according tothe embodiment. The lighting system 1200 shown in FIG. 6 is an exampleof a lighting system and the embodiment is not limited thereto.

Referring to FIG. 6, the lighting system 1200 may include a case body1210, a light emitting module 1230 installed in the case body 1210, anda connection terminal 1220 installed in the case body 1210 to receivepower from an external power source.

Preferably, the case body 1210 may include material having superior heatdissipation property. For instance, the case body 1210 includes metallicmaterial or resin material.

The light emitting module 1230 may include a substrate 700 and at leastone light emitting device package 600 installed on the substrate 700.According to an embodiment, although the light emitting module 1110 mayinclude the light emitting device package 600 installed on the substrate700, the light emitting device 100B according to the embodiment may bedirectly installed in the light emitting module 1110.

The substrate 700 may include an insulating member printed with acircuit pattern. For instance, the substrate 700 includes a PCB (printedcircuit board), an MC (metal core) PCB, an F (flexible) PCB, or aceramic PCB.

In addition, the substrate 700 may include material that effectivelyreflects the light. The surface of the substrate 700 can be coated witha color, such as a white color or a silver color, to effectively reflectthe light.

At least one light emitting device package 600 according to theembodiment can be installed on the substrate 700. Each light emittingdevice package 600 may include at least one LED (light emitting diode).The LED may include a colored LED that emits the light having the colorof red, green, blue or white and a UV (ultraviolet) LED that emits UVlight.

The LEDs of the light emitting module 1230 can be variously arranged toprovide various colors and brightness. For instance, the white LED, thered LED and the green LED can be arranged to achieve the high colorrendering index (CRI). In addition, a fluorescent sheet can be providedon the path of the light emitted from the light emitting module 1230 tochange the wavelength of the light emitted from the light emittingmodule 1230. For instance, if the light emitted from the light emittingmodule 1230 has a wavelength band of blue light, the fluorescent sheetmay include yellow phosphors. In this case, the light emitted from thelight emitting module 1230 may pass through the fluorescent sheet sothat the light is viewed as white light.

The connection terminal 1220 may be electrically connected to the lightemitting module 1230 to supply power to the light emitting module 1230.Referring to FIG. 6, the connection terminal 1220 may have a shape of asocket screw-coupled with the external power source, but the embodimentis not limited thereto. For instance, the connection terminal 1220 canbe prepared in the form of a pin inserted into the external power sourceor connected to the external power source through a wire.

According to the lighting system as described above, at least one of thelight guide member, the diffusion sheet, the light collection sheet, thebrightness enhancement sheet or the fluorescent sheet may be provided onthe path of the light emitted from the light emitting module, so thatthe desired optical effect can be achieved.

As described above, the lighting system may include a light emittingdevice or a light emitting device package having a reduced operatingvoltage and improved light efficiency, thereby obtaining superior lightefficiency and reliability.

Any reference in this specification to “one embodiment,” “anembodiment,” “example embodiment,” etc., means that a particularfeature, structure, or characteristic described in connection with theembodiment is included in at least one embodiment of the invention. Theappearances of such phrases in various places in the specification arenot necessarily all referring to the same embodiment. Further, when aparticular feature, structure, or characteristic is described inconnection with any embodiment, it is submitted that it is within thepurview of one skilled in the art to affect such feature, structure, orcharacteristic in connection with other ones of the embodiments.

Although embodiments have been described with reference to a number ofillustrative embodiments thereof, it should be understood that numerousother modifications and embodiments can be devised by those skilled inthe art that will fall within the spirit and scope of the principles ofthis disclosure. More particularly, variations and modifications arepossible in the component parts and/or arrangements of the subjectcombination arrangement within the scope of the disclosure, the drawingsand the appended claims. In addition to variations and modifications inthe component parts and/or arrangements, alternative uses will also beapparent to those skilled in the art.

What is claimed is:
 1. A light emitting device comprising: a firstconductive semiconductor layer; a second conductive semiconductor layer;and an active layer interposed between the first and the secondconductive semiconductor layers, wherein the first conductivesemiconductor layer, the active layer, and the second conductivesemiconductor layer include Al, wherein the second conductivesemiconductor layer has Al content higher than Al content of the firstconductive semiconductor layer, wherein the active layer includes aplurality of quantum well layers and a plurality of barrier layers,wherein the quantum well layers have Al content lower than Al content ofthe barrier layers, wherein the second conductive semiconductor layerincludes a first layer and a second layer, wherein the second layer ofthe second conductive semiconductor layer has a thickness of about 800 Åto about 1200 Å, and the first layer of the second conductivesemiconductor layer has a thickness of about 200 Å to 300 Å, and whereinAl content of the first layer is different from Al content of the secondlayer.
 2. The light emitting device of claim 1, wherein the firstconductive semiconductor layer has a composition formula ofAl_(x)Ga_(1-x)N (0.02≦x≦0.08).
 3. The light emitting device of claim 1,wherein the quantum well layers have a composition formula ofAl_(x)In_(y)Ga_(1-x-y)N (0≦x≦0.005, 0.1≦y≦0.3), and the quantum barrierlayers have a composition formula of Al_(x)Ga_(1-x)N (0.01≦x≦0.03). 4.The light emitting device of claim 1, wherein the second conductivesemiconductor layer has a composition formula of Al_(x)Ga_(1-x)N(0.1≦x≦0.3).
 5. The light emitting device of claim 1, further comprisinga buffer layer under the first conductive semiconductor layer, whereinthe buffer layer has a composition formula of Al_(x)Ga_(1-x)N (0.5≦x≦1).6. The light emitting device of claim 5, further comprising an undopedsemiconductor layer between the first conductive semiconductor layer andthe buffer layer, wherein the undoped semiconductor layer has acomposition formula of Al_(x)Ga_(1-x)N (0<x≦0.05)
 7. The light emittingdevice of claim 6, wherein the undoped semiconductor layer has a firstthickness in a range of about 0.5 μm to about 1 μm.
 8. The lightemitting device of claim 1, wherein the first layer of the secondconductive semiconductor layer without Al is formed on the active layerand the second layer of the second conductive semiconductor layerincluding Al is formed on the first layer.
 9. The light emitting deviceof claim 1, wherein Al content of the first conductive semiconductorlayer and Al content of the active layer are different from each other.10. The light emitting device of claim 1, further comprising: a secondelectrode on the second conductive semiconductor layer; and a firstelectrode on the first conductive semiconductor layer.
 11. The lightemitting device of claim 1, further comprising: a conductive supportmember on the second conductive semiconductor layer; and an electrodeunder the first conductive semiconductor layer.
 12. The light emittingdevice of claim 1, wherein the composition ratio of In is adjusted inthe quantum well layers so as to adjust the conglomeration degree of In.13. The light emitting device of claim 1, wherein each of the quantumwell layers includes a first layer including Al and a second layerformed on the first layer without Al.
 14. The light emitting device ofclaim 13, wherein the first layer of the quantum well layer includesAlInGaN and the second layer includes InGaN.
 15. The light emittingdevice of claim 13, wherein the first layer of the quantum well layerhas a thickness of about 5 Å and the second layer has a thickness ofabout 15 Å.
 16. The light emitting device of claim 1, wherein the secondconductive semiconductor layer further includes a third layer, andwherein Al content of the third layer is different from Al content ofthe second layer.
 17. The light emitting device of claim 16, wherein thefirst layer and the third layer of the second conductive semiconductorlayer are formed of GaN and the second layer of the second conductivesemiconductor layer is formed of AlGaN.
 18. The light emitting device ofclaim 16, wherein the third layer of the second conductive semiconductorlayer without Al is formed on the second layer of the second conductivesemiconductor layer.
 19. The light emitting device of claim 17, whereinthe third layer of the second conductive semiconductor layer has athickness of about 200 Å to 300 Å.
 20. The light emitting device ofclaim 1, wherein each of the quantum well layers has a plurality oflayers and at least one of the plurality of layers includes a layerwithout Al.
 21. A light emitting device package comprising: a packagebody; a first and a second electrode layers mounted on the package body;a light emitting device provided on the package body and electricallyconnected to the first and the second electrode layers, wherein thelight emitting device comprises: a first conductive semiconductor layer;a second conductive semiconductor layer; and an active layer interposedbetween the first and the second conductive semiconductor layers,wherein the first conductive semiconductor layer, the active layer, andthe second conductive semiconductor layer include Al and the secondconductive semiconductor layer has Al content higher than Al content ofthe first conductive semiconductor layer, wherein the active layerincludes a plurality of quantum well layers and a plurality of barrierlayers, and wherein the quantum well layers has Al content lower than Alcontent of the barrier layers, wherein the second conductivesemiconductor layer includes a first layer and a second layer, whereinthe second layer of the second conductive semiconductor layer has athickness of about 800 Å to about 1200 Å, and the first layer of thesecond conductive semiconductor layer has a thickness of 200 Å to 300 Å,and wherein Al content of the first layer is different from Al contentof the second layer.
 22. The light emitting device package of claim 21,wherein the first conductive semiconductor layer has a compositionformula of Al_(x)Ga_(1-x)N (0.02≦x≦0.08).
 23. The light emitting devicepackage of claim 21, wherein Al content of the first conductivesemiconductor layer and Al content of the active layer are differentfrom each other.
 24. The light emitting device package of claim 21,wherein the quantum well layers have a composition formula ofAl_(x)In_(y)Ga_(1-x-y)N (0≦x≦0.005, 0.1≦y≦0.3), and the quantum barrierlayers have a composition formula of Al_(x)Ga_(1-x)N (0.01≦x≦0.03). 25.The light emitting device package of claim 21, wherein the secondconductive semiconductor layer has a composition formula ofAl_(x)Ga_(1-x)N (0.1≦x≦0.3).
 26. The light emitting device package ofclaim 21, further comprising a buffer layer under the first conductivesemiconductor layer, wherein the buffer layer has a composition formulaof Al_(x)Ga_(1-x)N (0.5≦x≦1).
 27. The light emitting device package ofclaim 21, further comprising an undoped semiconductor layer between thefirst conductive semiconductor layer and the buffer layer, wherein theundoped semiconductor layer has a composition formula of Al_(x)Ga_(1-x)N(0<x≦0.05).
 28. The light emitting device package of claim 21, whereinthe composition ratio of In is adjusted in the quantum well layers so asto adjust the conglomeration degree of In.
 29. The light emitting devicepackage of claim 21, wherein each of the quantum well layers includes afirst layer including Al and a second layer formed on the first layerwithout Al.
 30. The light emitting device package of claim 29, whereinthe first layer of the quantum well layer includes AlInGaN and thesecond layer includes InGaN.
 31. The light emitting device package ofclaim 29, wherein the first layer of the quantum well layer has athickness of about 5 Å and the second layer has a thickness of about 15Å.
 32. The light emitting device of claim 21, wherein the first layer ofthe second conductive semiconductor layer without Al is formed on theactive layer and the second layer of the second conductive semiconductorlayer including Al is formed on the first layer.
 33. The light emittingdevice package of claim 21, wherein the second conductive semiconductorlayer further includes a third layer, and wherein Al content of thethird layer is different from Al content of the second layer.
 34. Thelight emitting device package of claim 33, wherein the first layer andthe third layer of the second conductive semiconductor layer are formedof GaN and the second layer of the second conductive semiconductor layeris formed of AlGaN.
 35. The light emitting device package of claim 21,wherein the undoped semiconductor layer has a first thickness in a rangeof about 0.5 μm to about 1 μm.
 36. The light emitting device package ofclaim 21, wherein the first layer of the second conductive semiconductorlayer without Al is formed on the active layer and the second layer ofthe second conductive semiconductor layer including Al is formed on thefirst layer.
 37. The light emitting device package of claim 33, whereinthe third layer of the second conductive semiconductor layer without Alis formed on the second layer of the second conductive semiconductorlayer.
 38. The light emitting device package of claim 33, wherein thethird layer of the second conductive semiconductor layer has a thicknessof about 200 Å to 300 Å.
 39. The light emitting device package of claim21, wherein the light emitting device is an ultraviolet (UV) lightemitting device that emits UV light.
 40. The light emitting devicepackage of claim 21, wherein the reflective layer includes at least oneof Ag, an alloy of Ag, Al, an alloy of AL, Pt, and an alloy of Pt. 41.The light emitting device package of claim 21, wherein each of thequantum well layers has a plurality of layers and at least one of theplurality of layers includes a layer without Al.
 42. The light emittingdevice package of claim 21, further comprising an electrode on the firstconductive semiconductor layer.
 43. The light emitting device package ofclaim 21, further comprising a reflective layer under the secondconductive semiconductor layer.
 44. The light emitting device package ofclaim 43, further comprising a conductive support member disposedbetween the reflective layer and the second conductive semiconductorlayer.
 45. The light emitting device package of claim 44, wherein theconductive support member includes at least one of Ti, Cr, Ni, Al, Pt,Au, W, Cu, Mo, and a semiconductor substrate implanted with impurities.